New structural faults have been discovered beneath the Atlantic Ocean, potentially heightening the risk of significant earthquakes and tsunamis that could impact the region. This finding is based on a recent study published this week in Natural Earth Science.

For centuries, the reason behind Portugal’s susceptibility to major earthquakes, despite its distance from prominent fault lines, has puzzled scientists.

On November 1, 1755, Lisbon was struck by a catastrophic earthquake registering 8.7 on the Richter scale, resulting in the deaths of tens of thousands and triggering a tsunami that reached the Caribbean. In 1969, a magnitude 7.8 tremor off the Portuguese coast killed 25 individuals.

“One of the challenges is that these earthquakes occur on completely flat plains and are distant from fault lines,” stated Professor Joan Duarte, a geologist at the University of Lisbon and the study’s lead author, as reported in BBC Science Focus.

“Following the 1969 earthquake, it became clear that there were signs of a subduction belt, indicating something unusual in that region.”

The subduction zone, where one tectonic plate moves under another, is responsible for some of the planet’s most destructive “megathrust” earthquakes, including the catastrophic events in the Indian Ocean in 2004 and Tohoku in 2011. However, the Atlantic Ocean has traditionally been viewed as relatively stable, with its plates slowly drifting along the mid-Atlantic ridge.

Duarte’s team compiled earthquake records and utilized computer models from the Horseshoe Abyss Monkey Plain, a deep seabed located southwest of Portugal. They uncovered evidence that the mantle—a hot, dense layer beneath the Earth’s crust—is undergoing a process known as peeling.

“The base of the plate is separating as if peeling off, like the sole of a shoe,” Duarte explained. “The first moment of realization came when I thought, ‘Oh, there’s something out there.’ The second was when our computer models confirmed this peeling process.”

This phenomenon is unusual in oceanic crust, which typically behaves like a “crème brûlée,” resting on a more pliable layer below due to its rigid buoyancy.

In this instance, it appears that water has been infiltrating the rock for millions of years, chemically weakening it and enabling the mantle mass to descend toward the Earth’s depths.

The research suggests that we might be witnessing the emergence of a new subduction zone in the Atlantic Ocean, which could ultimately reunite Africa, Europe, and the Americas into future supercontinents.

For now, however, the immediate concern is the potential for earthquakes.

“A significant earthquake will occur again,” Duarte emphasized.

“If there’s a forecast for rain tomorrow, you’d take an umbrella,” he added. “We don’t need to know the exact time of the rain, just that we must be prepared.”

“The same goes for earthquakes. While we can’t predict when major ones will strike, we understand the likelihood, so we need to be ready.”

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About our experts

Joan Duarte is an assistant professor of tectonics at the University of Lisbon and serves as the president of the Department of Tectonics and Structural Geology within the European Union of Geosciences. His research has been featured in journals such as Geophysical Research Letters, Nature Communications, and Geology.